When an abnormal area of tissue, such as a tumor, is discovered by non-invasive means, a tissue diagnosis is often required in order to determine the appropriate treatment. This requires that an adequate sample of tissue be removed from the patient for histopathological analysis. The tissue may be obtained in a variety of ways, such as surgical excision, fine needle aspiration biopsy or large needle core biopsy.
Fine needle aspiration biopsy, using needles with diameters of 20–22 Gauge, is minimally invasive. Typically, a biopsy needle with a stylet is inserted into the abnormal tissue, under the guidance of an imaging modality, such as ultrasound or magnetic resonance imaging (“MRI”). The stylet is then removed. A syringe is attached to the needle, suction is applied through the syringe and then the needle is manually thrust into and out of the tissue to capture and remove cellular material. However, rather than cutting the tissue to enable collection in the needle bore, the thin needle tends to displace the tissue, especially rigid malignant tissue. Therefore, only a small number of cells may be obtained. Even after repeated attempts, a sufficient amount of tissue might not be obtained. Displacement of tissue also alters the frame of reference defined by the imaging modality.
To improve yield, large bore needles, having diameters of 18–10 Gauge, have been used. However, the risk of damage to the tissues that the needle has to traverse to reach the area of pathology, as well as the risks of bleeding, infection and patient discomfort, rise with increasing needle thickness. Healing time may therefore be increased. Large needle core biopsy needles may also cause significant damage to certain organs, such as the lungs and the spleen. As with fine needles, displacement of movable tissues, such as breast tissue, is also a problem.